Treatment methods for corrosion pits on the outer wall of boiler tubes

The outer wall of boiler tubes is frequently exposed to high temperatures, high pressure, and chemical environments, making it vulnerable to various forms of corrosion and pitting. These issues not only compromise the performance of boiler systems but also pose serious safety risks if left unaddressed. Below are the primary causes of corrosion on the outer wall of boiler pipes and effective treatment methods.

Main Causes of Corrosion on the Outer Wall of Boiler Tubes

1. Acid Corrosion

Acidic substances present in steam, feedwater, or chemical agents can gradually erode the pipe's outer surface. In particular, when carbon steel boiler tubes are exposed to acidic environments—common in some industrial applications—they are highly prone to acid corrosion, which accelerates material degradation and surface pitting.

2. Oxidation Corrosion

Long-term exposure to high temperatures causes oxidation reactions on the steel surface. These reactions form oxide layers of varying thickness, which may flake off unevenly, leading to oxidation pits, cracks, and other surface defects. This type of thermal oxidation corrosion is inevitable in high-temperature environments such as power plants and refineries.

3. Electrolytic (Discharge) Corrosion

Electrostatic discharge in boiler pipelines can cause electrolytic reactions on the metal surface. This results in localized corrosion pits, especially in sections of the pipe where electrical grounding is poor or where insulation breaks down.

Treatment Methods for Boiler Tube Outer Wall Corrosion Pits

1. Surface Cleaning and Restoration

For mild surface corrosion, cleaning is often the most cost-effective solution. Using chemical cleaning agents or abrasive tools, the corroded layer can be removed, restoring a smooth pipe surface. This is particularly effective for small hydraulic tubes or precision boiler tubes, where restoring surface integrity can significantly extend service life without affecting performance.

2. Active Protection Technology

When corrosion is detected early, active corrosion protection can help prevent further deterioration. Based on anodic protection principles, this method involves applying a controlled voltage to the pipe’s outer surface to inhibit corrosion pit development. This technique is especially useful for high-value components such as heat exchanger tubes and drill pipes, reducing the need for costly repairs or replacements.

3. Repair Welding

In cases where corrosion pits are deep or widespread, repair welding becomes necessary. This involves selecting filler materials that match the pipe’s base metal and conducting thorough surface pretreatment to ensure welding quality. Proper welding techniques can restore structural integrity and prolong the tube’s operational lifespan.

4. Pipe Replacement

If corrosion is extensive and cannot be remedied by welding, pipe replacement is the most reliable solution. Replacement pipes must match the original specifications and material grade. After installation, the system should undergo pressure testing and quality inspections to ensure safe and reliable operation.

Conclusion

Timely and effective management of boiler tube outer wall corrosion is essential to ensure the safety and efficiency of boiler systems. The methods listed above—ranging from cleaning to full replacement—should be selected based on the severity and extent of corrosion. Additionally, routine inspection and maintenance play a key role in early detection, helping to minimize downtime and avoid costly failures.